WhatsApp for Samsung Galaxy Grand Prime Plus

If the phone is signed into a Google account, the fastest route is Find My Device (google.com/android/find) signed into that same account, where you can remotely Erase the device and set it up fresh. To wipe it manually, power off, then hold Volume Up + Home + Power together until the recovery menu appears, choose Wipe data/factory reset with the volume keys and confirm with the Power button. Note that on this older Android 6 device you'll need the previously synced Google account credentials afterward to clear the Factory Reset Protection (FRP) lock. See how others solved this on Reddit

Go to Settings > Apps, and for heavy apps like Facebook, Chrome and Gallery tap Storage > Clear cache to free up its tiny internal storage. Then disable bloatware you don't use via Settings > Apps > (select app) > Disable, and reduce animations through Developer options (unlock it by tapping Settings > About phone > Build number seven times) by setting Window, Transition and Animator scales to 0.5x. After backing up your data to Google Drive and Google Photos, a factory reset often restores noticeable responsiveness on aging units. See how others solved this on Reddit

This model ships with only 8GB internal storage, so insert a microSD card, then move media via Settings > Apps > (app) > Storage > Change to SD card where the app allows it, and set the Camera app to save to SD card. Offload photos by enabling backup in the Google Photos app, then use its Free up space option to delete already-backed-up copies. Regularly clearing app caches under Settings > Apps helps keep enough room for Play Store updates. See how others solved this on Reddit

Install Samsung Smart Switch on the old phone (it's built into newer Galaxy models under Settings > Accounts and backup > Bring data from old device) and transfer wirelessly over Wi-Fi, which avoids needing a cable adapter for this micro-USB phone. For contacts and calendar, first confirm they're synced under Settings > Accounts > Google so they reappear automatically on the new phone. Photos move cleanly if you've backed them up in Google Photos beforehand and sign into the same account on the new device. See how others solved this on Reddit

Open the Play Store, tap the profile/menu, then Settings > Parental controls to limit app installs by content rating with a PIN. Turn off installs from unknown sources via Settings > Lock screen and security > Unknown sources so sideloaded APKs are blocked. You can also remotely locate the phone and, if needed, lock or erase it through Find My Device tied to that Google account. See how others solved this on Reddit

Use Samsung Smart Switch, which has an iOS mode that imports contacts, calendar and photos by signing into your iCloud account directly in the app. Before starting, back up your iPhone to iCloud and, if you used iMessage, turn it off at Settings > Messages > iMessage on the iPhone so future SMS texts reach your Samsung. As an alternative for photos, install Google Photos on both devices, or download your library from iCloud and re-sync it through your Google account. See how others solved this on Reddit